Show Hints / Candidates will help you see the available pencil values within the cell, row, column, and boxes.

Sudoku How To Technique: X Wing

Taking the process of elimination to the next level we introduce the strategy of “this one hint value shows up two times in two different of the same PRIMARY ROW or COLUMN CONTAINER, and also intersect using the alternate ROW or COLUMN CONTAINER. Giving the knowledge that that HINT value cannot be valid anywhere else within that alternate container”. The primary CONTAINER cannot have more than two of the valid hint for this method to work.

Taking a look at the diagram below, reviewing COLUMNS C3 and C8. Both COLUMNS have two CELLS with HINT values of {4}, both existing on the same ROWS R2 and R8 (which is the key). Because of that knowledge we know that HINT value {4} must be present in either CELL R2C3 and R2C8 within ROW R2 within the final solution, and the alternate combination within ROW R8, allowing us to eliminate the HINT value {4} within CELL R2C1, R8C1 and R8C9.

Side Notes:
This rule works because COLUMN C1 has the HINT value of {4} in more than 2 CELLS.

This solving method has been categorized as Very Hard Sudoku. Try this and other Very Hard Sudoku solving methods.
Try this X Wing Sudoku puzzle.